Re: No exceptions?

From: Jon Heggland <>
Date: Fri, 30 Jun 2006 09:58:55 +0200
Message-ID: <e82lnp$k12$>

Bob Badour wrote:
> The extend operation creates a new relation by adding an attribute to an
> existing one. Strictly speaking, whether the candidate key would be
> preserved depends on the operation used to derive the extended
> attributes. Ungrouping a relation valued attribute, for instance, would
> affect the key. However, most familiar extend operations would not.

I think it is a bit misleading to consider ungroup an example of extend. For one thing: The extend operator as normally defined does not affect cardinality; ungroup does (in general).

Received on Fri Jun 30 2006 - 09:58:55 CEST

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